Bugfix: with-pvars must be called after binding the pvar, not before.

README.md

@@ -1,3 +1,18 @@
 stxparse-info
 =============
-README text here.
+
+The module `stxparse-info/parse` is a patched version of `syntax/parse` which
+tracks which syntax pattern variables are bound. This allows some libraries to
+change the way syntax pattern variables work.
+
+For example, `phc-graph/subtemplate` automatically derives temporary
+identifiers when a template contains `yᵢ …`, and `xᵢ` is a pattern
+variable. To know from which `varᵢ` the `yᵢ …` identifiers must be derived,
+`phc-graph/subtemplate` needs to know which syntax pattern variables are
+within scope.
+
+To use this package, simply require `stxparse-info/pares` instead of
+`syntax/parse` Additionally, it is possible to use the for-syntax function
+`(current-pvars)` from `stxparse-info/current-pvars` to access the list of
+currently-bound pattern variables, and the macro `(with-pvars (pvar ...)
+. body)` can be used to add new pattern variables to the list.

parse/private/runtime.rkt

@@ -96,14 +96,14 @@ residual.rkt.
                     (map parse-attr (syntax->list #'(a ...)))])
        (with-syntax ([(vtmp ...) (generate-temporaries #'(name ...))]
                      [(stmp ...) (generate-temporaries #'(name ...))])
-         #'(with-pvars (name ...)
+         #'(letrec-syntaxes+values
+               ([(stmp) (make-attribute-mapping (quote-syntax vtmp)
+                                                'name 'depth 'syntax?)] ...)
+               ([(vtmp) value] ...)
              (letrec-syntaxes+values
-                 ([(stmp) (make-attribute-mapping (quote-syntax vtmp)
-                                                  'name 'depth 'syntax?)] ...)
-                 ([(vtmp) value] ...)
-               (letrec-syntaxes+values
-                   ([(name) (make-syntax-mapping 'depth (quote-syntax stmp))] ...)
-                   ()
+                 ([(name) (make-syntax-mapping 'depth (quote-syntax stmp))] ...)
+                 ()
+               (with-pvars (name ...)
                  . body)))))]))
 
 ;; (let-attributes* (([id num] ...) (expr ...)) expr) : expr

scribblings/stxparse-info.scrbl

@@ -45,4 +45,21 @@ know which syntax pattern variables are within scope.
 
  This can be used to implement macros which work similarly to
  @racket[syntax-parse] or @racket[syntax-case], and have them record the syntax
- pattern variables which they bind.}
+ pattern variables which they bind.
+
+ Note that the identifiers @racket[pvar ...] must already be bound to syntax
+ pattern variables when @racket[with-pvars] is used, e.g.
+
+ @racketblock[
+ (let-syntax ([v₁ (make-syntax-mapping depth (quote-syntax valvar))]
+              [v₂ (make-syntax-mapping depth (quote-syntax valvar))])
+   (with-pvars (v₁ v₂)
+     code))]
+
+ instead of:
+
+ @racketblock[
+ (with-pvars (v₁ v₂)
+   (let-syntax ([v₁ (make-syntax-mapping depth (quote-syntax valvar))]
+                [v₂ (make-syntax-mapping depth (quote-syntax valvar))])
+     code))]}

test/test-current-pvars.rkt

@@ -16,4 +16,26 @@
               '([y x] [z w y x]))
 
 (check-equal? (list-pvars)
-              '())
+              '())
+
+;; Check that the identifier has the right scopes
+(define-syntax (ref-nth-pvar stx)
+  (syntax-case stx ()
+    [(_ n)
+     (number? (syntax-e #'n))
+     #`#'#,(let ([pvar (list-ref (current-pvars) (syntax-e #'n))])
+             (datum->syntax pvar (syntax-e pvar) stx))]))
+
+(check-equal? (syntax-parse #'1
+                [x
+                 (syntax->datum (ref-nth-pvar 0))])
+              1)
+
+(check-equal? (syntax-parse #'1
+                [x
+                 (cons (syntax->datum (ref-nth-pvar 0))
+                       (syntax-parse #'2
+                         [x
+                          (list (syntax->datum (ref-nth-pvar 0))
+                                (syntax->datum (ref-nth-pvar 1)))]))])
+              '(1 2 1))